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From left: Penn State biochemistry and molecular biology professor Song Tan, and Schreyer Scholars Turner Pecen and James Johnston, worked to develop DNA plasmids that can be used to produce DNA ladders.

Image: Jeff Rice

Climbing the ladder

Climbing the ladder

UNIVERSITY PARK, Pa. — Turner Pecen didn’t have a lot of lab experience when he came to Penn State as a freshman in 2013. The project he spent much of his college career working on could change that for future high school students.

Pecen, as part of a team that included fellow Schreyer Scholar alumni James Johnston and Ryan Henrici, published a paper with Professor of Biochemistry and Molecular Biology Song Tan in the journal Scientific Reports on the research they did on two circular forms of DNA plasmids that can be used to produce base pair DNA ladders, which function as rulers to measure the size of DNA fragments.

The plasmids will be available without licensing restrictions for use by scientists around the world at a fraction of the cost of commercially available DNA ladders.

“If this can actually be distributed to these smaller labs or lower-funded labs, it can really push science forward,” said Pecen, who graduated in May after majoring in biochemistry and molecular biology, and immunology and infectious diseases. “They can use hundreds of dollars a year on other things that they may make breakthroughs with.”

Tan and Henrici, who graduated from Penn State in 2015 and is currently a Marshall Scholar studying at the London School of Hygiene and Tropical Medicine, had the idea of nesting the fragments so that the same two plasmids would produce different sets of ladders depending on the restriction enzyme used. The team, including Johnston and Pecen, spent three years creating the plasmids — named pPSU1 and pPSU2 — through a series of cloning steps.

“Once you get it once, you can just transform it back into E.coli, and produce more of it on your own,” said Johnston, a May graduate and double major in biochemistry and molecular biology, and statistics. “You don’t need to spend money on it again, which is the neat thing.”

Both Scholars turned their attention to thesis work for much of the past year, but both believe the work on the project and with Tan made them more diligent — and resilient — scientists.

“The biggest thing I’ve gained from this project was that failure is a part of science and it’s to be expected,” Pecen said. “You can really understand how good you are at experiencing failure and how good you are at picking yourself back up and moving forward.”

For more than a month, Pecen was stuck on the same segment, and could not get it to work. Figuring out a way to find the solution was an experience he doesn’t think he would have been able to find in another lab or organization on campus.

The students learned from Henrici, who would always be at his bench on the weekends, what it meant to throw themselves fully into a project. They learned from Tan’s attention to detail and what it takes to put a manuscript together from the ground up, and he made sure they not only were able to get results but also that they understood the processes that made the results possible.

“You learn that you have to be your own harshest critic,” Johnston said. “You’re going through territory that isn’t frequently traversed. If you take a lab class at Penn State, almost every experiment that you do is going to work every time because they’re optimized completely and picked as things you do in that lab class because they do work.

"This project kind of set the stage for our thesis work, where things don’t always go as you planned."

Johnston is taking a gap year and then plans to attend medical school. Pecen is off to Harvard for graduate school. They are grateful for the opportunity to challenge themselves and to be a part of a project that could have broad impact.

“It’s a steep learning curve,” Pecen said, “but it was a great experience.”